1. Field of the Invention
The invention relates to a multistage rotary pump comprising a substantially closed, elongated pump body which is provided at one of its extremities with a base element containing suction and pressure connecting pieces and at its other extremity with a top element and which is surrounded in spaced relationship by a jacket to form an annular return volume, and clamping devices joining the jacket to the base element and the top element, the jacket being sealed with respect to these elements and being provided at least substantially close to its two extremities with contact shoulders of stable form which are acted upon by the clamping devices.
2. Description of the Prior Art
A motor-pump assembly is described in German Pat. No. 35 23 599, in which the thin-walled jacket of the motor housing is provided with a contact shoulder which co-operates with a clamping ring which is thrust against the contact shoulder by means of spring force. This clamping joint for connecting the motor section and pump section is costly to produce, since the thin-walled jacket of the motor section has to be reduced in its terminal portion by turning in several stages, in order to form a stable contact shoulder. Furthermore, the thin-walled jacket has to be very carefully chucked in a lathe to be able to produce a precisely fitting contact shoulder.
Another generally known solution of joining the jacket to the terminal pump elements comprises clamping the jacket between the terminal elements by mean of tension rods, the tension rods being screw-coupled to the terminal elements. Since flat joints are commonly clamped between the jacket extremities and the terminal elements in the case of this solution, the problem exists of excessive compression of the flat joints when a pump fluid flows past the jacket particularly at very high temperature and the latter consequently expands correspondingly in length, because the tension rods which are spaced from the jacket thus understandably do not accompany the longitudinal expansion to the same degree. This results in a destruction of the flat joints in the course of time.